1. Field of Use
This disclosure is generally directed to fuser members useful in electrophotographic imaging apparatuses, including digital, image on image, and the like. This disclosure also relates to processes for making and using fuser members.
2. Background
In a typical electrophotographic imaging apparatus, an image of an original to be copied, or the electronic document image, is recorded in the form of an electrostatic latent image upon a photosensitive member and the latent image is subsequently rendered visible by the application of thermoplastic resin particles or composites thereof, which are commonly referred to as toner. The visible toner image is in a loose powdered form and can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a substrate or support member support, which may be a cut sheet or continuous media, such as plain paper.
The use of thermal energy for fixing toner images onto a support member is well known. In order to fuse toner material onto a support surface permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to be firmly bonded to the support.
Several approaches to thermal fusing of toner images have been described in the prior art. These methods include providing the application of heat and pressure substantially concurrently by various means: a roll pair maintained in pressure contact; a belt member in pressure contact with a roll; and the like. Heat may be applied by heating one or both of the rolls, plate members or belt members. The fusing of the toner particles takes place when the proper combination of heat, pressure and contact time is provided. The balancing of these parameters to bring about the fusing of the toner particles is well known in the art, and can be adjusted to suit particular machines or process conditions.
During operation of a fusing system in which heat is applied to cause thermal fusing of the toner particles onto a support, both the toner image and the support are passed through a nip formed between the roll pair, or plate or belt members. The concurrent transfer of heat and the application of pressure in the nip affect the fusing of the toner image onto the support. It is important in the fusing process that no offset of the toner particles from the support to the fuser member take place during normal operations. Toner particles that offset onto the fuser member may subsequently transfer to other parts of the machine or onto the support in subsequent copying cycles, thus increasing the background or interfering with the material being copied there. The referred to “hot offset” occurs when the temperature of the toner is increased to a point where the toner particles liquefy and a splitting of the molten toner takes place during the fusing operation with a portion remaining on the fuser member. The hot offset temperature or degradation to the hot offset temperature is a measure of the release property of the fuser member, and accordingly it is desirable to provide a fusing surface, which has a low surface energy to provide the necessary release.
A fuser or image fixing member, which can be a roll or a belt, may be prepared by applying one or more layers to a suitable substrate. Cylindrical fuser and fixer rolls, for example, may be prepared by applying an elastomer or fluoroelastomer to an aluminum cylinder. The coated roll is heated to cure the elastomer. Such processing is disclosed, for example, in U.S. Pat. Nos. 5,501,881; 5,512,409; and 5,729,813; the disclosure of each of which is incorporated by reference herein in their entirety.
Fuser members may be composed of a resilent silicone layer with a fluoropolymer topcoat as the release layer. Fluoropolymers can withstand high temperature (>200° C.) and pressure conditions and exhibit chemical stability and low surface energy, i.e. release properties. For instance, fluoroplastics, such as TEFLON® from E.I. DuPont de Nemours, Inc. have a lower surface energy due to high fluorine content and are widely used for oil-less fusing.
Fluoroplastics, such as PTFE and PFA, can be applied by coating technique onto a fuser member substrate to form a release layer. Since fluoroplastics typically require high baking temperatures (i.e. over 300° C.) to form a continuous film, which is well above the decomposition temperature of silicone rubber (about 250° C.), the processing window for forming a fluoroplastic topcoat over a silicone-containing substrate to achieve uniform coatings without defects is extremely narrow. Cracks and bubbles are the two major defects observed during the fabrication of such fuser members.